In numerous areas of technology, such as robotics or medicine, for example, it is often desirable or necessary to topographically map an object or a part of the body, and such mapping is often achieved through some sort of tactile responsive imaging system. One type of conventional tactile sensor that is used to determine a location or, more specifically, the shape of an object comprises an array of conductors separated from a second array of conductors by a dielectric. For instance, in U.S. Pat. No. 4,549,093 of Severwright and in U.S. Pat. No. 5,055,838 of Wise et al., an array of column conductors is separated from an array of row conductors by a dielectric and a two dimensional shape of an object is determined according to the locations at which the row conductors contact the column conductors or where the capacitance between conductors varies. In U.S. Pat. No. 5,225,959 of Stearns, a tactile sensor comprises an array of sensor capacitors that produces outputs corresponding to the pressure applied at each of the capacitive sensors by apparently varying the magnitude of each capacitance in proportion to the magnitude of the pressure.
Another type of tactile sensor, such as disclosed in U.S. Pat. No. 4,405,197 of Bejczy and in U.S. Pat. No. 4,733,068 of Thiele et al., uses an array of transmitting optical fibers and an array of receiving optical fibers to determine a location or shape of an object. An object coming in contact with this type of sensor varies the amount of light carried by the receiving optical fiber, whereby a shape of the object may be determined.
A third type of tactile sensor has a plurality of passages through which a signal medium, such as air, is conducted. When an object comes in contact with this type of sensor, a two dimensional shape of the object may be determined by monitoring the amounts of the signal medium flowing through the passages. The tactile sensor in U.S. Pat. No. 4,306,148 of Ringwall et al. and the opto-mechanical touch sensor in U.S. Pat. No. 4,599,908 of Sheridan et al. are examples of this type of sensor.
Many of the conventional tactile sensors as discussed in the foregoing, however, suffer from a disadvantage in that they are incapable of producing a high resolution image of an object or sensing surface topography more than a few millimeters deep. For the most part, the resolution of these sensors is dependent upon the number of elements making up the sensor, and generally it is not possible to have in a given area, enough elements to produce high resolution. Further, many of these tactile sensors can only determine the location of an object or produce, with proper processing, a two dimensional image of an object and are incapable of producing a synthesized three dimensional image of the object. By "synthesized three dimensional" is meant a perspective rendition of an image on a two dimensional screen such that the width, height, and depth of the image can be observed.
For example, the tactile sensor in the Ringwall et al. patent is used in the field of robotics for determining the magnitude of a force. During operation of this tactile sensor, the air flow in each passage deflects a metallic tab whose angular displacement is related to the magnitude of a force acting on the sensor. A light beam is directed onto the metallic tab and the quantity of light deflected off of the metallic tab represents the magnitude of the force. U.S. Pat. No. 4,982,611 of Lorenz et al., U.S. Pat. No. 5,010,773 of Lorenz et al., and U.S. Pat. No. 5,261,266 of Lorenz et al. disclose the use of strain gauges on a robotic hand to determine certain forces and torques.
The prior art sensors for use in robotics, however, are typically used to determine the magnitude of forces or torques and are incapable of producing a high resolution image of an object or sensing surface topography more than a few millimeters deep. As a result, the end-effectors in robotics cannot easily determine the position of an object nor easily identify an object. Therefore, for example, when robotics are used to assist in a manufacturing process, only a single type of part is typically delivered to the end-effectors with the position and timing of the part's delivery accurately controlled. Thus, there is a need in the art for a tactile image mapper that may be used in robotics to acquire a high resolution topographical image of an object which would enable the end-effectors to identify an object and determine the positioning of the object.
Another disadvantage of conventional tactile sensors discussed is the lack of conforming compliance due to the thinness of the sensing layer where only small surface displacements can be sensed. In medical applications, there is a need to sense surface displacements up to a few centimeters.